The older, more common vaccine (which protects against strains A, C, W-135 and Y) works by training the body's immune cells to recognize the sugar on the meningitis-causing bacteria as something bad, Orenstein tells Shots.

The same approach won't work for the B-type bacteria.

When immune cells encounter the meningitis B sugar coating, they're more likely to identify it as belonging to a friend rather than a foe, Orenstein says. They're used to seeing the same sugar all over the human cells.

There are ways to teach our immune system that the meningitis B coating is bad, but that could be risky, he says. In the hunt for meningitis bacteria, the immune system could start attacking human cells by mistake.

The obvious solution is to train the immune system to recognize meningitis B by some other characteristic. But there are hundreds of strains, and sometimes the only thing they all have in common is that darned sugar coating.

Dr. Andrin Oswald, head of Novartis' vaccine and diagnostics unit, says researchers analyzed the genes of hundreds of meningitis B strains before they found a few chemicals that most of the strains seemed to share.

"But substrates are different around the globe," Oswald tells Shots. And even within a single country, the meningitis strains can change over time. Even so, some protection is better than none, and Oswald says he hopes the FDA will approve Bexsero for broader use in the U.S. sometime soon.

Oswald says the Novartis vaccine protects against at least 70 percent of meningitis B strains — and up to 95 percent of strains in some countries.

So Bexsero's not perfect. But Emory's Orenstein says at the moment the Novartis vaccine seems like the best bet. "I think it's as good as we can get for now," he says. "Certainly if I had a kid at Princeton, I'd want my kid to get the vaccine."

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.